Process fluid or gas bearings are now being utilized in an increasing number of diverse applications. These fluid bearings generally comprise two relatively movable elements with a predetermined spacing therebetween filled with a fluid such as air, which, under dynamic conditions, form a supporting wedge sufficient to prevent contact between the two relatively movable elements.
More recently, improved fluid bearings, particularly gas bearings of the hydrodynamic type, have been developed by providing foils in the space between the relatively movable bearing elements. Such foils, which are generally thin sheets of a compliant material, are deflected by the hydrodynamic film forces between adjacent bearing surfaces and the foils thus enhance the hydrodynamic characteristics of the fluid bearings and also provide improved operation under extreme load conditions when normal bearing failure might otherwise occur. Additionally, these foils provide the added advantage of accommodating eccentricity of the relatively movable elements and further provide a cushioning and dampening effect.
The ready availability of relatively clean process fluid or ambient atmosphere as the bearing fluid makes these hydrodynamic, fluid film lubricated, bearings particularly attractive for high speed rotating machinery. While in many cases the hydrodynamic or self-acting fluid bearings provide sufficient load bearing capacity solely from the pressure generated in the fluid film by the relative motion of the two converging surfaces, it is sometimes necessary to externally pressurize the fluid between the bearing surfaces to increase the load carrying capability. While these externally pressurized or hydrostatic fluid bearings do increase the load carrying capacity, they do introduce the requirement for an external source of clean fluid under pressure.
In order to properly position the compliant foils between the relatively movable bearing elements, a number of mounting means have been devised. In journal bearings, it is conventional practice to mount the individual foils in a slot or groove in one of the bearing elements as exemplified in U.S. Pat. No. 3,615,121.
To establish stability of the foils in most of these mounting means, a substantial pre-load is required on the foil. That is, the individual foils must be loaded against the relatively movable bearing element opposed to the bearing element upon which the foils are mounted. It has been conventional to provide separate compliant stiffener elements or underfoils beneath the foils to supply this required preload as exemplified in U.S. Pat. Nos. 3,893,733 and 4,153,315.
In order to facilitate start-up and to reduce bearing wear, the bearing surfaces of the individual foils may be coated with a high lubricity material such as a stratified fluorocarbon, molybdenum disulfide, graphite fluoride, or the like. The use of such coatings, while enhancing the life of the foil bearing, introduces certain operating temperature limitations thereon. As still higher temperature environments are envisioned for foil bearing operation, the temperature limitations of these coatings become critical since they cannot survive as high a temperature as the underlying generally metallic foil. Thus, higher temperature coatings must be developed or means found to limit the operating temperature at the coated foil bearing surfaces. Examples of prior cooling schemes for foil thrust bearings can be found in U.S. Pat. Nos. 4,227,753 and 4,247,155 and in U.S. patent application Ser. No. 656,399, filed Oct. 1, 1984 by Alston Lee-Van Gu entitled "Foil Thrust Bearing Cooling" and assigned to the same assignee as this application, now U.S. Pat. No. 4,621,930.